ADVANCED ICON DESIGN: COMPOUND ICONS (MODIFIERS)

Summary from the TLDR Design newsletter

Compound icons combine a base symbol with a modifier (such as a plus, lock, or slash) to communicate more specific actions or states, making them especially useful when icons appear without text labels or need to distinguish similar items. While effective, they also introduce challenges: limited space can reduce legibility, combining symbols creates ambiguous visual "grammar," and similar compound icons can become difficult to tell apart at a glance. Use clear visual separation between the base and modifier, simplify icons where context allows, and always test them for readability in their intended size and interface.